I currently admin a site, which as it stands right now is simply a php/MYSQL based online catalog for products we sell here in our showroom, but we're discussing the possibility of adding a shopping cart to allow people to be able to make purchases online and have them delivered.

We're a single store here and have no immediate plans to ship beyond our local delivery area, so my plan is to implement a table in our database which will list all the zip codes that we do deliver to. So what I'd like to do is to simply implement a shopping cart button on our product pages, and obviously give people the option to check out securely and if necessary have delivery - provided their zip code coincides with the ones listed in that table that we do deliver to. I'd really rather not have to completely change the site over to accomodate the ability to make purchases - but obviously I'm open to any suggestions.